Process for cleaning metal objects



United States Patent Olice 3,094,469 Patented June 18, 1963 3,094,469 PROCESS FOR CLEANING METAL BJECTS Wennemar Strauss and Hans Wedell, Dusseldorf-Holthausen, Germany, assignors to Dehydag Deutsche Hydrierwerke G.m.b.H., Dusseldorf, Germany, n corporation of Germany Filed July 6, 1959, Ser. No. 825,327 Claims priority, application Germany July 12, 1958 12 Claims. (Cl. 204-141) This invention relates to a method for cleaning metal surfaces prior to electroplating. It more particularly relates `to a method wherein organic solvents and aqueous cleaning solutions are -used in sequence.

For the quality of metal electroplates, especially for their adherence to the `hase metal, the cleaning process to which the objects to be electroplated are customarily subjected is of importance. Normally, the oiled metal objects or those which come from the polishing machine and are contaminated with polishing paste and metal dust are first subjected to a cleansing or washing procedure with organic solvents, such as trichloroethylene or perchloroethylene. This step is sometimes carried out manually `and sometimes in automatic devices. During this step the major portion of the oily decontamination goes into the solvent. The treated objects are then dried, This primary cleaning step is in most cases followed by a defatting procedure by boiling, preferably under alkaline conditions, in addition to a subsequent electrolytic defatting procedure. After passing through a rinsing step the objects are electroplated or they may be subjected to another type of surface treatment, such as phosphatizing, eloxadizing and the like.

The disadvantage of this cleansing process is particularly the operation with organic solvents such as trichloroethylene. In addition to the annoyance of the bad odor, persons who work with these solvents are continuously subjected to possible damage to their health due to inhalation of chlorohydrocarbon vapors, which in the beginning shows itself by coughing, dizziness, lowering of `the blood pressure and vomiting and may finally lead to damage of the kidneys, liver and brain.

It has `been attempted to overcome these disadvantages `by using expensive technical apparatus, such as trichloroethylene scrubbers or exhaust devices, but in many cases it is not possible to do Without a manual trichloroethylene scrubbing procedure, particularly if the metal objects are highly profiled and comprise narrow depressions. A greater disadvantage of the above described multi-step cleansing procedure is that the process is space-consuming due to the great number of treatment vats and tubs and because it is awkward and time-consuming due to the length and interruption of the treatment sequence.

lt is an object of this invention to provide a method for cleansing sheet metal wherein the release of fumes of the organic cleaning agent will be eliminated.

`It is a further object to provide a cleansing method wherein the use of `multiple cleaning vais is not necessary, and cleansing may be accomplished in one vat.

it is a further object of this invention to provide a cleansing method wherein the cleaning time is greatly reduced.

Another object of this invention is to provide a method for cleansing metals with organic solvents and aqueous cleansing agent solutions, and in the presence of surfaceactive agents, in the same vat.

These and other objects of our invention will become apparent as the description thereof proceeds.

We have now found that the tabove disadvantages can be avoided and the objects of our invention attained if the cleansing procedure is carried out with a bath consisting of two layers, the lower of which consists of one or more fat-dssolving organic solvents, especially chlorohydrocarbons, and the upper layer consists of one or more aqueous cleansing agent solutions, preferably adjusted to alkaline reaction. The layers may also contain surface active substances. The objects to be cleaned are lirst treated in the organic solvent llayer and subsequently in the aqueous cleansing agent layer and are then rinsed in customary fashion. In order to improve the cleansing effect, the metal objects may be agitated in customary fashion either in the lower andor upper layer. Furthermore, the cleansing procedure in the aqueous cleansing -layer may, as customary, .be performed with the yaid of an electric current, and this layer and possibly also the organic solvent layer may be heated. Moreover, the organic solvent layer and, if desired, also the aqueous cleansing agent layer, may be circulated and, if necessary, filtered. The quantitative or volumetric ratio which is used in these two layers depends upon the type and size of the objects and also on the type and extent of the contamination. It is attempted to use the organic solvents as economically vas possible, and in most cases two parts by volume of organic solvent for every three parts Aby volume of aqueous cleansing agent are used, lbut more or less of the organic solvent may also be employed,

More particularly, the process is carried out in the following manner: The metal object to be cleaned, made of iron, steel, copper, brass, bronze, nickel or another metal or of a corresponding alloy, is introduced into a treatment vat which contains the two layers of cleansing agents. The metal object is first introduced into the lower layer or organic solvent which has the greater specific weight. Suitable organic solvents are, for example, carbon tetrachloride, trichloroethylene, perchloroethylene, mixtures of chlorinated hydrocarbon solvents and 'mixtures of hydrocarbons with chlorinated hydrocarbons.

After a short residence period, which may last Afor about 0.5 to 5 minutes, or even longer, the object is lifted into the aqueous layer above the organic layer, which contains preferably alkaline reacting cleaning agents.

Examples of such cleansing agents are, as customary, alkali metal hydroxides, soda, water glass, phosphates, cyanides and the like. The quantity of cleansing agent is generally from l() gm. per liter to gm. per liter. The aqueous layer may further be modified with known substances which act as dispersing agents or as contamination carriers, such as carboxy methyl cellulose and the like. ln general, the substances which are usually used as industrial cleansing agents and mixtures thereof may be used for this purpose.

We have further found that a substantial improvement and acceleration of the degreasing and cleansing procedure can be achieved if the aqueous cleansing layer or the organic solvent layer or both layers of the cleansing bath are modied with surface active substances.

The use of the additives produces a surprisingly rapid wetting elfect when the metal object to be cleaned is transferred from the organic layer to the aqueous layer. The liquid films which are released during the wetting action carry with them the major portion of the contaminating substances adhering to the surface and thus substantially contribute to an acceleration of the cleansing effect.

Examples of suitable surface-active substances are cation-active, anion-active or non-ionic substances; it is advantageous to use primarily hydrophilic agentsY in the aqueous layer and primarily organophilictagents in the organic layer, in order to avoid a mixing of the layers or an emulsilication upon agitation of the objects in the bath. A few examples of such surface active substances which may be used in accordance with the invention are listed below.

(1) Technical grade oleyl alcohol (iodine No. 50/ 55) condensed with 2 mols ethylene oxide.

(2) Technical grade oleyl alcohol (iodine No. 50/ 55 consensed with mols ethylene oxide.

(3) Technical grade oleyl alcohol (iodine No. 50/55) condensed with l2 mols ethylene oxide.

(4) A fatty alcohol mixture obtained by hydrogenation of fatty acids from beef tallow condensed with 4 mols ethylene oxide.

(5) A fatty alcohol mixture obtained by hydrogenation of fatty acids from beef tallow condensed with 30 mols ethylene oxide.

(6) A fatty alcohol mixture with 12 to 18 carbon atoms obtained by hydrogenation of fatty acids from coconut oil, condensed with 2 mols ethylene oxide.

(7) A fatty alcohol mixture with 12 to 18 carbon atoms obtained by hydrogenation of fatty acids from coconut oil condensed with 8 mols ethylene oxide.

(8) Nonylphenol condensed with 2 mols ethylene oxide.

(9) Nonylphenol condensed with 4 mols propylene oxide.

(10) Nonylphenol condensed with l() mols ethylene oxide.

(ll) Dinonylphenol condensed with 4 mols ethylene oxide.

(12) Dinonylphenol condensed with l0 mols ethylene oxide.

(13) Lauric acid amide condensed with 10 mols ethylene oxide.

(14) Ethanolamides of fatty acids from coconut oil condensed `with 4 mols ethylene oxide.

(l5) Castor oil condensed with 16 mols ethylene oxide.

(16) A mixture of hexadecyl and dihexadecylphosphate condensed with 5 mols ethylene oxide.

(17) An alkylamine mixture the alkyl radicals of which originate from the fatty acids of beef tallow, condensed with 12 mols ethylene oxide.

(18) Decyl alcohol condensed with 3 mols ethylene oxide.

(19) Technical grade oleic acid condensed with 15 mols ethylene oxide.

(20) Sorbitol ester of oleic acid condensed with 8 mols ethylene oxide.

(2l) Octylthiophenol condensed with 10 mols ethylene oxide.

(22) Oleic acid condensed with 1 mol saccharose.

(23) The sodium salt of n-dodecylbenzenesulfonate.

(24) The methoxypropylamine salt of tetrapropylenebenzenesulfonate.

(25) The sodium salt of tetrapropylenebenzenesulfonate.

(26) The sodium salt of laurylsulfate.

(27) The sodium salt of a sulfonated nonylphenol.

(28) The ethanolamine salt of a sulfated addition prod uct of 1 mol nonylphenol and 2 mols ethylene oxide.

(29) The sodium salt of a sulfated addition product of 1 mol nonylphenol and 4 mols ethylene oxide.

(30) The sodium salt of a sulfated addition product of 1 mol technical grade oleyl alcohol and 3 mols propylene oxide.

(3l) The potassium salt of an alkyl-N-methyl alanide, the alkyl radical of which originates from the fatty acids of coconut oil.

(32) The sodium salt of a sulfated addition product of l mol lauric acid monoethanolamide and 4 mols ethylene oxide.

(33) The sodium salt of an albumin-fatty acid condensation product.

(34) The potassium salt of palm oil fatty acids.

(35) The sodium salt of a carboxymethylated addition product of one mol tetradecyl alcohol and 8 mols ethylene oxide.

(36) The diethanolamine salt of a phosphated addition product of l mol decylalcohol and 3 mols ethylene oxide.

(37) The sodium salt of a phosphated fatty alcohol mixture which was obtained by hydrogenation of the fatty acids contained in palm oil.

(38) The sodium salt of sulfated butylester of ricinoleic acid.

(39) The Sodium salt of diisopropylnaphthalene sulfonate.

(40) The sodium salt of sulfosuccinic acid di-n-decylester.

(41) The sodium salt of a sulfonated olefinic mixture with 12 to 18 carbon atoms.

(42) The potassium salt of an N-hexadecyl-taurin.

(43) Cetylpyridinium-bromide.

(44) Hexacedylcarboxymethyl-oxyethyl-morpholiniumchloride.

(45) An alkylaminoacetate mixture (alkyl radicals from the fatty acids contained in beef tallow).

(46) The amide formed by lauric acid and ,f3-aminoethyldiethyl-methylammonium methosulfate.

(47) p-Stearophenyl-trimethylarnmonium-methosulfate.

(48) Hexadecylarnine-laurate.

(49) The reaction product formed by methyl chloride with the adduct of 3 mols ethylene oxide with technical grade stearyl amine.

(50) Cetyldimethyl-sulfonium-rnethosulfate (5 l N-allyl-Soctylthiuronium-propionate.

(52) N-oxethyl-N'phenyl-S-dodecyl-thiuronium bromide.

As already indicated earlier, the selection of the surface-active substances will depend primarily upon their solubility in the aqueous or organic layers. The concentrations to be used depend substantially upon the bath conditions, that is upon the manner in which the bath is being operated, from the degree of contamination, etc. The concentrations are between the range of 0.05 to 10 gm. per liter, and as a rule quantities of 0.1 to 3 gm. per liter are used. Excessive concentrations may enhance emulsification and are therefore not advantageous.

In order to accelerate the cleansing process, the aqueous layer may simultaneously or subsequently `be operated as a cathodic or anodic degreasing bath in which the objects to be electroplatcd are cleansed with the aid of an electric current. For `this purpose, electrodes are mounted in the treatment vat within the range of the aqueous layer.

The treatment in the aqueous layer also takes a relatively short time, about 0.5 to 5 minutes. The metal obiects which are withdrawn from the aqueous layer are satisfactorily degreased and cleaned and may be rinsed in yaccordance with known methods and thereafter be passed on to further treatment, such as to an electroplating treatment. The advantage of this novel method of operation resides primarily in that only 1 vat is needed instead of the heretofore customary minimum of 2 vats, and furthermore, in that the presence of an aqueous layer over the chlorohydrocarbons prevents the penetration of vapors from these onganic solvents into the atmosphere and therefore lthe damaging effects connected therewith, since these substances are insoluble in water. Finally, this combined utilization of the two layers produces a complete utilization of the `reaction energy at the interface, which considerably increases and accelerates the cleansing effect.

The invention may be better understood by reference to the drawing which show examples of suitable apparatus which may be used for practicing the process in accordance with the invention, and in which,

FIGURE l shows a vat 1 in the upper portion of which cleansing metal sheets or articles.

FIGURE 2 illustrates a method and apparatus for cleansing continuous metal strip, wires and the like.

FIGURE 1 shows a vat l in the upper portion of which a pair of electrodes 2 are mounted and which comprise rails 3 for the supply of current, said rails also serving as supports for the metal objects 4 to be electroplated The organic solvent layer A occupies the lower portion of `the vat, while the aqueous cleansing solution B occupies the upper part. Rails 3 are provided with any suitable support means and may be raised or lowered to enable objects 4 t0 be treated in both layers A and B. The upper portion of the vat is provided with a heating jacket 5, but in place of this jacket an internal heating device, for example one comprising electric heating elements, may be provided. In the lower portion of the vat a screen insert 6 is provided above the oor to separate the contaminations. In order to circulate the lower layer of the bath liquid and for tiltration of the bath liquid a circulating line 7, with pump 8 and filter 9 is provided in the lower portion. The upper portion of the container may be provided with the same circulating de vice, but it may also be fashioned in the manner illustrated in the drawing. In accordance with FIGURE l, the principal vat 1 comprises an over-flow 14 with container 10 in which contaminating substances from the surface of the upper aqueous layer are trapped and rinsed away. From there the bath liquid is returned to the upper portion of the vat through the circulating line 11 and lilter 13 with the aid of pump 12. The circulating lines may also have feed lines, not shown, for replenishment of the bath liquid.

FIGURE 2 shows the apparatus for the treatment of endless metal objects, for example of wires, ribbons, chains and the like. it consists of a U-shaped vat 1a which contains the organic solvent layer A and the aqueous cleansing agent layer B in communicating equilibrium. The right-hand arm oi the U-shaped container contains the aqueous cleansing agent layer and is provided with electrodes 2 and heating jacket 5. The endless material 4a to be cleansed is passed through the bath over rollers 15, rst through layer A and subsequently through layer B. The current feed line 3a is connected to the guide roller 15a mounted above the right arm of the vat. The speed of movement of material 4a and the length of vat 1e can be made to provide a suitable residence time in the bath.

In the examples below, special data for the performance of the process according to the invention are given and a list of combinations of surface active agents is shown as they are advantageously used in the process according -to the invention. lt should be understood that these examples are `for the purpose of illustrating our invention to persons skilled in the art and are not intended to be limitative.

Example 1 An oily and dirty object made of brass is introduced through the aqueous layer of a Z-phase cleansing bath into the perchloroethylene layer. After a period of ex'- posure of 2 minutes the brass object is lifted into the aqueous phase which contains 50 gm. per liter soda, 45 gm. per liter sodium hydroxide and 0.05 gm. per liter carboxyrnethyl cellulose, and is cathodicaliy degreased therein for l minute at 3G to 35 C. under the action of an electric current. After this treatment the brass object is free from oil, clean and may be electroplated after passing through a customary rinsing step.

The cathodic cleansing step was also applied to brass, copper, nickel, bronze and iron in connection with nickel electroplating, with similar results. In the case of iron and all types of steel, prior to copper electroplating, it is advantageous to apply an anodic degreasing procedure.

Example II For the purpose of cleaning an object made of copper which is highly contaminated with oil, polishing paste and metal clust, it is iirst introduced into the lower layer of a cleansing bath which contains perchloroethylene modified with 0.5 gm. per liter of a condensation product of oleyl alcohol and mols ethylene oxide. After barely two minutes of treatment a considerable portion of the oily and wax-like contaminations are removed from the copper surface. Thereafter, the object is placed into the upper aqueous layer which contains 0.5 gm. per liter tetrapropylene-benzene-sodium sulfonate in addition to 50 gm. per liter soda, 45 gm. per liter sodium hydroxide and 0.5 gm. per liter carboxy methyl cellulose. Due to the wetting effect the residual contaminations are rapidly removed thereby. The contaminations removed in the aqueous layer do not remain in this phase but sink into the organic layer, enveloped by ohloroethylene, without emulsificatlon taking place. After about 1 minute the object is withdrawn from the bath and is rinsed. The object can now electroplated. Without the addition of the surface active compounds, the cleansing process requxres approximately twice the amount of time.

The copper object may also be degreased under the actron of an electric current during its residence time in the aqueous layer l1n the apparatus described in the principal patent, .the object serving as the cathode. This method, in addltion to producing an improvement of the cleansing effect, has the advantage that shorter treatment periods can be used. Example III Sheet metal made of iron, copper, zinc or brass which was highly contaminated with oil and metal dust was cleaned in a vat which contained a layer of perchloroethylene and above this organic layer an aqueous layer containing 50 gm. per liter soda, 45 gm. per liter sodium hydroxide and 0.5 gm. per liter carboxymethy-l cellulose. Both of the layers were modied with the surface-active substances indicated 1n the list below; the list also shows the quantitative ratios of the surface-active additives. The quantitative data are based on 100% active substances. 'I he numbers of the products refer to the numbers in the list given 1n `the disclosure above.

Orgaxliic vSolvent Aqueous Cleaning Bath Composition No. er Agent Layer Product No' g [l Prgzuct gjl.

1 1.0 7 40 i 1.0 23 gg 3 1 0.5 30 2.5 2 0.5 2 0.5 2 0.3 40 0.5 2 0.3 10 0.5 2 0.2 25 1.0 2 0.a 20 0.2 2 0. 5 28 1 2 0.3 40 0.2 e 2.5 1s 0.2 s 0.3 10 0.5 s 0.3 31 0. 2 s 0.3 33 0. 2 0.3 s i3 5i Sil 0 0.3 5 0.3 0 0. 2 17 0.5 11 0.5 12 0.1 16 3.0 so 0.2 23 0.3 22 05 342 g'i 23 0.3 7 0.a 23 0.3 1s 0.2 23 0.a 23 0.1 24 0.3 24 0.2 24 0.3 25 0.1

. 7 a7 0.3 15 iig 31 0. 5 23 0.2 3s 0.3 a1 0.3 3s 0.3 as 04 2 as 0.3 41 0.a 3s 0.2 s1 0.3 40 0.3 5 0.2 40 0.3 10 0.3 40 0.3 21 0.2 40 0.2 23 0. 3 40 0.3 40 0. 2 40 0.3 42 0. s 4a 1.0 s 0.3 s it m 43 10 2s iig 4s 2.5 34 0.3 40 1.0 27 0.2 52 1.0 ss 0.2

The sheet metal was treated in each layer for 1 to 2 minutes; an extraordinary cleansing effect was achieved.

Emulsification did not occur. Without the use of the surface-active agents, at least twice the cleansing period is required in all cases.

While we have set forth specific embodiments `an-d preferred modes of operation of our invention, it will be understood that these are only for the sake of illustration and that various changes and modifications may be made without departing from the disclosure and the scope of the appended claims.

We claim:

1. A process `for cleansing metal surfaces by the use of chlorohydrocarbon solvents and aqueous cleansing agent solutions, in .a cleaning bath comprising a lower layer of said chlorohydrocarbon solvent and an upper layer of said aqueous cleansing agent solution, the steps comprising treating said metal surfaces first in said chlorohydrocarbon solvent layer and subsequently in said aqueous cleansing agent solution and thereafter rinsing said metal surfaces.

2. The process of claim 1 wherein the cleaning in the aqueous layer is carried out under the action of an electric current.

3. The process of claim 1 wherein the metal surfaces are agitated while in said bath.

4. The process of claim 1 wherein heat is provided at least to the aqueous layer of the bath.

5. The process of claim l wherein at least the organic solvent layer is recirculated and filtered.

6. The process of claim l wherein the bath is modified with surface-active substances.

7. The process of claim 6 wherein the aqueous layer is modified with hydrophilic surface-active substances.

8. The process of claim 6 wherein the organic solvent layer is modified with organophilic surface-active substances.

9. A process for cleansing metal surfaces by the use of chlorohydrocarbon solvents and aqueous alkaline cleansing agent solutions, in a cleaning bath comprising a lower layer of said organic solvent and an upper layer of said aqueous cleansing agent solution, the `steps comprising treating said metal surfaces first in said organic solvent `layer and subsequently in said aqueous cleansing agent solution and thereafter rinsing said metal surfaces.

10. A process for cleansing metal surfaces by the use of chlorohydrocarbon solvents and aqueous cleansing agent solutions, in a cleaning bath comprising a lower layer of said chlorohydrocarbon solvent land an upper layer of said aqueous cleansing agent solution, the steps comprising treating said metal surfaces first in said chlorohydrocarbon solvent layer `and subsequently in said aqueous cleansing agent solution under the infiuence of `heat and electric current and thereafter rinsing said metal surfaces, wherein said metal surfaces are agitated during treatment, and each of said layers is recirculated and filtered.

1l. A process for cleansing metal surfaces by the use of chlorohydrocarbon solvents and aqueous cleansing agent solutions, in `a cleaning bath comprising `a lower layer of said chlorohydrocarbon solvent and an upper layer of said aqueous cleansing agent solution, the steps comprising treating said metal surfaces first in said chlorohydrocarbon solvent layer in the presence of an organophilic surface-active substance and subsequently in said aqueous cleansing agent solution in the presence of a hydrophilic surface-active substance and under the influence of heat and electric current, and thereafter rinsing said metal surfaces, wherein said metal surfaces are agitated during treatment, and each of said layers is recirculated and filtered.

12. A process for continuously cleansing metal surfaces by the use of chlorohydrocarbon solvents and aqueous cleansing agent solutions, comprising the steps of providing a bath consisting of a lower layer of a chlorohydrocarbon solvent and a superimposed layer of `an aqueous cleansing agent solution, passing said metal objects sequentially first through said chlorohydrocarbon solvent layer and then through said aqueous cleansing agent solution and thereafter rinsing.

References Cited in the file of this patent UNITED STATES PATENTS 781,230 Rodman Ian. 31, 1905 1,004,673 Monnot Oct. 3, 1911 2,077,332 Kroll Apr. 27, 1937 2,313,422 Dimon Mar. 9, 1943 2,372,599 Nachtman Mar. 27, 1945 2,487,399 Thurber Nov. 8, 1949 2,556,017 Vonada June 5, 1951 2,653,883 Thomas Sept. 29, 1953 2,683,692 Harris July 13, 1954 2,778,791 Duncan Ian. 22, 1957 2,953,507 Palme Sept. 20, 1960 2,957,782 Boiler Oct. 25, 1960 FOREIGN PATENTS 725,186 Germany Sept. 16, 1942 OTHER REFERENCES Silman; Metal Industry, November 24, 1944, pages 330-32.

Mitchell: The Cleaning of Metal (1930), Magnus Chemical Company, pages 12-14. 

1. A PROCESS FOR CLEANSING METAL SURFACES BY THE USE OF CHLOROHYDROCARBON SOLVENTS AND AQUEOUS CLEANSING AGENT SOLUTIONS, IN A CLEANING BATH COMPRISING A LOWER LAYER OF SAID CHLOROHYDROCARBON SOLVENT AND AN UPPER LAYER OF SAID AQUEOUS CLEANSING AGENT SOLUTION, THE STEPS COMPRISING TREATING SAID METAL SURFACES FIRST IN SAID CHLOROHYDROCARBON SOLVENT LAYER AND SUBSEQUENTLY IN SAID AQUEOUS CLEANSING AGENT SOLUTION AND THEREAFTER RINSING SAID METAL SURFACES.
 2. THE PROCESS OF CLAIM 1 WHEREIN THE CLEANING IN THE AQUEOUS LAYER IS CARRIED OUT UNDER THE ACTION OF AN ELECTRIC CURRENT. 